Liquid crystal displays, especially in the form of TN (twisted nematic) or STN (super twisted nematic) displays are widely used. Because of the threshold voltage required for switching a display element, these liquid crystal systems are suitable for multiplex control. Larger displays, in particular for laptop screens, which have more than 105 display elements (pixels), can be produced with the aid of thin film field transistor technology (TFT). For display technology, see Ullmann""s Encyclopaedia of Industrial Chemistry, vol. A 15, 1990, page 272 to 277 and page 359 to 391, and vol. A 8, page 619 to 621.
Liquid crystal display is based on a change in the direction of the optical axis in a layer of a birefringent organic liquid of almost crystalline arrangement effected by application of an electrical field. On passing through the liquid crystal layer, polarised light undergoes a rotation of the plane of polarization. If the polarized light which has passed through the liquid crystal layer is viewed through a second polarization film, light/dark contrasts result, depending on the rotation of the plane of polarization of the light.
A black/white or grey scale contrast which is as far as possible non-coloured is aimed for here. Because of the phase difference between the ordinary and extraordinary light ray, however, certain wavelengths of the white light spectrum are extinguished. This is counteracted by the phase difference being compensated for by means of xcex/4 to xcex/2 platelets. However, compensation of the phase difference is achieved only in the region of small angles of observation. It has therefore also already been proposed to achieve the phase compensation by additional liquid crystal layers which are not stimulated by electrical fields. U.S. Pat. No. 5,472,635 thus proposes employing a nematic liquid crystal below the glass transition temperature, the nematic phase being frozen-in. EP-A 646 829, on the other hand, proposes employing a layer of a low molecular weight discotic liquid crystal as the phase compensation layer.
Disadvantages of these proposals are that on the one hand high requirements regarding the thickness of the liquid crystal layer are to be imposed, and furthermore additional transparent carrier plates, between which the liquid crystal layer is accommodated, are required.